1. Field of the Invention
The invention relates to an address generator for generating addresses enabling a memory to output its stored data in a predetermined sequence and in particular to an address generator capable of generating addresses enabling a memory to output its data stored along parallel lines angularly disposed to the orthogonally arranged storage elements of the memory.
2. Prior Art
It is well known in the art, that image data can be electrically stored in an electronic memory such as a read only memory or random access memory. The memory stores individual pixels of image data in discrete storage elements disposed at the intersections of the orthogonally arranged rows and columns and each storage element has a unique address which defines its location. The address conventionally contains the identity of the row and column which contain the particular storage element.
A visual image of the information electrically stored in the memory is generated by sequentially addressing the individual storage elements along each row one row at a time from the top of the memory to its bottom in synchronization with the scan raster of a display device such as a cathode ray tube as taught by Evans et al in U.S. Pat. No. 4,179,693. Obviously the image may be inverted by addressing the individual storage elements in the reverse order from bottom to top or the image may be rotated by 90.degree. by addressing the storage elements along the columns in the desired sequence.
Often it is desired to rotate the displayed image at an angle intermediate the four orthogonal positions discussed above. To achieve such an intermediate rotation of the image, the prior art as disclosed by Gennetten in U.S. Pat. No. 4,245,321, teaches a rotating raster generator. This rotating raster generator generates input signal to the cathode ray tube's deflection coils which rotate the raster of the cathode ray tube so that the scan lines are rotated with respect to the physical geometry of the cathode ray tube. This same effect could also be obtained by physically rotating the deflection coils as is known in the art. Rotation of the scan raster is generally only applicable to monochromatic display devices, such as a black and white cathode ray tube. Rotation of the scan raster is not applicable to multi-color displays such as a color cathode ray tube because it changes the relationship between the mutli-color dot pattern and the scan lines resulting in the loss of the color information.
In the field of photogrammetry where the stored image data is taken from a photographic image having known abberations and distortions, Whiteside et al in U.S. Pat. No. 3,973,243 teaches an address generator which generates addresses in the memory in a special order different from the order in which the data elements are stored in the memory to remove the known distortions. This address generator is incapable of addressing the memory along parallel lines angularly disposed to the orthogonal orientation of the rows and columns of storage elements.
The disclosed invention is an address generator capable of generating addresses which lie along parallel lines angularly disposed with respect to the orientation of the rows and columns of storage elements in the memory.